1. Field of Invention
This disclosure is in the field of Laser Radar coherent target detection and imaging.
2. Description of the Related Art
Laser Detection and Ranging (LADAR) uses phase coherent processing at light frequencies to acquire targets within its detection range. Typically, both the velocity and location of a target is the result of the detection process. The principles of LADAR are detailed in the prior art as exemplified by G. C. Bachman in Laser Radar Systems and Techniques Artech House, 1979, incorporated herein in its entirety by reference.
LADAR operation is at optical frequencies. These are higher than RADAR microwave frequencies. Thus, compared to RADAR, LADAR uses different concepts, has a theoretical larger bandwidth and higher angular resolution. Operating at optical frequencies, orders of magnitude greater than microwaves, LADAR poses unique advantages and limitations.
One aspect of the complexities of LADAR high frequency operation is the spatial coverage of a transmitted pulse. Unlike the wide dispersion of microwave RADAR frequencies directed and focussed by large antennas, LASER based LADAR emits and detects tightly collimated, narrow LASER energy. Thus, the illumination/reception pattern of a single LADAR pulse has limited solid angle coverage. This limited angular coverage forces LADAR systems to emit multiple pulses and make multiple scans to cover a volume where a target of interest might be located.
Multiple redundant LADAR pulses are also required by signal to noise considerations. LADAR signal to noise reception is sensitive to target reflectivity as well as atmospheric conditions. High humidity, dust, a specular rather than reflective target dictate redundant pulses per unit volume. The constraint of limited angle coverage combined with the need for redundant pulses extends target acquisition time for LADAR within a search volume. Because of these constraints, LADAR search times of a volume may be lengthy, where a fast target may traverse the volume before detection.